Is Butterfly Bush Invasive? Should we plant it in urban areas?

Photo courtesy of Duke University

Say it isn’t so.  Butterfly bush is invasive and shouldn’t be planted? This is undoubtedly a touchy subject for many who love the flowers that attract butterflies throughout the summer.  It is a widely planted species and is known for attracting the showy swallowtail butterflies.  It is very easy to grow and widely available in the nursery trade.  But, and here is the big but – it is an invasive, exotic species.  What you may ask?  I have never seen it where it has escaped into the wild so it just can’t be invasive in Kentucky.  What got me thinking about writing this blog piece was a discussion amongst Kentucky Native Plant Society Members on Facebook on whether or not it should be planted and whether or not it is invasive. And to top it all off, there was an article in Birds and Blooms magazine that discussed how butterfly bush was an invasive exotic! This particular writer acknowledged in New Jersey that it had completely taken over dune vegetation and completely altered this natural community.  Even the state of Oregon bans the sale of this plant. Who would have known.

 The commonly species planted, Buddleia davidii, has escaped and has become a pest species in the Pacific Northwest (Oregon and Washington) and along the eastern Seaboard and in 1997 the Brooklyn Botanical Garden listed it as invasive.  If you look at the current distribution of where it has been found, it is moving west from the eastern seaboard states and is now found in most of the states surrounding Kentucky and in Kentucky as well.  It prefers riparian or streamside habitats and disturbed sites and in Kentucky I have seen it along the Ohio River and near the stream at Bad Branch State Nature Preserve in Letcher County.  The largest invasive problems appear to be in the Appalachian mountains all the way from New York through Alabama (in the Cumberland Plateau).  While this species is still not a major threat in Kentucky, we do know the best method of dealing with invasive plants, is to not let populations get established.  So here are the arguments made by folks for continued planting of this species.

I haven’t seen it escape on my five acres of land and it is therefore not invasive.  Here is the response to that question.  Buddleia, like many invasive species, has small windblown seeds that are dispersed far and wide. Once in the seed bank those seeds sit and wait, for just the right opportune moment and then, bingo, a problem seemingly develops overnight. A couple of examples will serve to highlight this.  A landscape architect friend vehemently disagreed with me that miscanthus (plume grass) was invasive because he had planted many in his rural yard and did not see any seedlings.  I explained the issue of small windblown seeds (or seeds dispersed by birds like the bush honeysuckles) and they travel long ways in search of appropriate habitat.  Not to be believed he told me.  A couple of years later, driving out by the farm I noticed an entire field of miscanthus and it was miles from his land with no other source plants available.  Where did it come from?  The Heavens?  A second example will solidify this concept.  Japanese spirea is a horribly invasive species and has been planted as an ornamental shrub for probably decades in this state.  It is now a problem and becoming a huge issue in natural areas.  I actually had a graduate student looking at control methods in the Big South Fork National River and Recreation Area.  It reverts from its cute compact form into a tall, rank, straggly natural form that is rhizomatous and takes over streamside forests, which it was doing in the BSFNRRA and was threatening two endangered plant species.  There was no source population for miles around. Just this spring  I was on the top of Pine Mountain, miles and miles from any source of Japanese spirea, and guess what; there is was, growing in several clumps, expanding into the forest unchecked. In another case I had a homemaker ask what the pink shrub in the woods and pasture was at their farm.  She described it and it was Japanese spirea and she indicated her husband, a beef cattle farmer, was none too happy because the cows wouldn’t eat it and the patches were getting larger.  How long did it take this species to become a problem in Kentucky?  We knew it was a problem in the Appalachian Mountains and along the Blue Ridge, but no one seemed to notice what was happening in Kentucky.  What happens is the seeds are blown here and there and then they sit in the soil, in the case of buddleia, it appears for decades.  Then, when conditions are appropriate, they germinate and the process of invasion has begun.  So just because you do not see them escaping in your yard doesn’t mean they aren’t invasive in the larger landscape and have not created a problem from your plants, miles and miles away unbeknownst to you.

The second argument was that native plant enthusiasts often create more issues for using natives because of their lack of compromise, sometimes confrontational approach, and strength of conviction about using exotic plants.  Furthermore, when dealing with the general public you need to have early success for attracting butterflies or wildlife in urban biological deserts or on school yards.  I would agree with the sentiments about some native plant enthusiasts, they sometimes do go too far and are too confrontational and I often think some compromise can be made with some species or there may be alternative solutions available to solving a particular issue. In almost all cases however, there are native plant materials that will do the same function in the landscape as the exotic. I do however take some issue with early success and buddleia being the source of that early success.  Given what one or two butterfly bushes cost, one could easily purchased several purple coneflowers, boneset, joe-pye-weed, New England aster plants and a couple of mints and could easily attract as many or more species that the butterfly bushes.  The species primarily attracted to butterfly bushes are the swallowtails and silver spotted skipper; whereas, the species attracted to the others include the swallowtails but also many other smaller species like hairstreak, snouts, red admirals, fritillaries, etc.  Furthermore, from the perspective of school yards, butterfly bushes flower in the summer, not the fall or spring when students are actually attending classes and therefore it is much better to plant those natives.  Even if you choose not to plant natives, old time single petaled zinnias and Mexican sunflowers are better butterfly attractors than is butterfly bush.  I have helped with the annual butterfly count for many years here in Central Kentucky and there has not been a year when we have seen more species, and more individuals, on native flowers than on butterfly bushes at the arboretum.

The next argument is that butterfly bush is very drought tolerant and may be the only source of nectar available for butterflies.  Hogwash.  Supposedly someone wrote that butterfly bushes produce more nectar than other species during drought. I could not find any scientific evidence to back this statement up.  None, not a single one.  One study, which was unpublished, done at Clemson examined the different content of nectar among butterfly bush varieties and found those with higher sugars of a particular type were visited more often, but the sample sizes are tiny, the study was not replicated, and never published in the scientific literature and they do not compare buddleia to other native species.  What we do know is that from one British study that nectar in butterfly bushes in Great Britain doesn’t differ between other nectar plants. Doug Tallamy, entomologist at Deleware State University calls butterfly bush “junk food” probably because of high sugar levels.  But high sugar levels are not the most important part of nectar.  A number of studies have documented it is the amino acids (that build protein) are the critical factor and it is linked to higher larval survival.

The next argument is that there are now sterile cultivars of this plant available that will not reproduce. My question is, how did they make it sterile?  By breeding or by genetic manipulation? We know that some plants, mostly annuals, can be genetically manipulated to suppress reproduction but it is often much more difficult in a perennial plant.  For example, paper companies are attempting to develop a genetically sterile cultivar of eastern cottonwood trees such that they can apply herbicides over the top of them and reduce growing costs.  They have only been at these more 20 or more years and they just can’t get them completely sterile.  We have been down this road before. I remember not that long ago when folks begged and pleaded with the Kentucky Nursery and Landsacpe Association to stop selling purple loosestrife. They said it was a very desirable plant and they would continue to sell it  because the new “sterile” hybrids did not escape.   How’s that working out for us?  This plant is now a serious problem in Kentucky, and I mean serious.  One day coming out of the mountains into a drainage of the Red River in Powell County I was greeted with an entire field of at least 40 acres in size of purple loosestrife.  It has escaped out of Louisville and has moved down the Ohio River and is beginning to threaten our native wetlands.  The audacity of some who continue to contend it just isn’t so is amazing.   In one case, there were plants growing in a stream immediately adjacent to the plantsman’s business and have moved down Hickman Creek and in one pond in town the entire shallow area was inundated with purple loosestrife from this release in just TWO YEARS.  The ironic thing is the plantsman denied they came from their plants!  Or how about those sterile cultivars of callary pears we were sold?  How’s that working out for you as you drive by ornamental pear forests now?  You get the point. The ultimate goal of all plants is to make new plants.

Finally, with all the other major environmental problems we face, global climate change, pollution, loss of biodiversity, etc. why pick on using this one little ol plant? I remember an old Chinese saying, “Every journey begins with a single step.”  We do have many important environmental problems but somewhere we have to set an example, do simple things to make a broader statement and to think globally and act locally. We all have to find where we can make a difference and the use of exotic plant material is ultimately a moral choice, just like choosing to change light bulbs, or reduce water consumption, or car pool, or whatever.  It comes down to each of our own choices; do we choose to knowingly use a plant that is or could become an invasive and harm the environment?  Only you can make that choice and if it becomes a problem then you know that you were not part of the solution, but rather part of the problem and what did your actions teach our young people that will inherit the earth after we are long gone? But just remember this, native plants saved the wine industry, saved the corn industry, provide us with the genetic material for 40% of our pharmaceuticals, etc. As I said, your option to grow this plant or any invasive exotic species is a moral and ethical choice. So, say it isn’t so, you can have your cake and eat it too and there is such a thing as a free lunch, ecologically speaking?   I doubt it but we can all convince ourselves because of course we are all reasonable people.  But just remember, reasonable people can reason just about anything.